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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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412                                 ALASKAN GLACIER STUDIES
It is known definitely that this portion of the Chugach Mountains had severe avalanches during the Yakutat Bay earthquakes of September, 1899, for the shocks were-felt with much severity on the Copper River delta southwest of Childs Glacier, as well as to the southeast; and many avalanches were heard in the Chugach Mountains to-the northwest.1 In all probability avalanches were also caused by the smaller Chugach earthquake of October 9, 1900, which was felt with much severity on the Copper River delta,8 and indeed by one party between Childs and Miles Glaciers. The rapidity of movement of this wave of advance in 1910 and its rapid diminution strongly suggests-the earthquake avalanche origin.
The climatic situation regarding Childs Glacier may be summarized as follows: At Fort Liscum near Yaldez, 60 miles northwest of Childs Glacier there was increased snowfall in 1902-1903 and in 1907-1908 (see table, p. 316). At Orca, S3 miles southwest of Childs Glacier, the snowfall8 was much heavier than usual in 1902-1903 and. from 1906 to 1908. For the snow year 1907-1908 the railway engineers' records at Miles Glacier station show a snowfall of 433 inches and for 1908-1909 of 410 inches. In the latter year the snowfall at Flag Point, 20 miles south of Childs Glacier was-355 inches. During the first half of the snow-year 1909-1910 the snowfall at Miles. Glacier station was 102| inches, or only half as much as in the corresponding months, of the two previous years. This suggests that the snowfall in 1907-1908 was exceptionally great. The slow advances of Miles and Grinnell Glaciers in 1910, of Heney Glacier in 1911, and of Allen Glacier in 1912, described on subsequent pages of this book, suggest that the advances of all five of these glaciers may be due to increased snowfall in 1902-1903 or 1906-1908, but the junior author does not feel that a sufficient body of fact is as yet available for choosing between the climatic and earthquake hypotheses.
The Terminal Moraine of Childs Glacier. There is unmistakable evidence that Childs: Glacier formerly spread out in a great bulb, similar to the present bulbs of Allen, Sheridan, and Miles Glaciers. The proof of this is found in the remnants of the great terminal moraine of Childs Glacier. There are five of these residual masses of glacial drift around the periphery of the former bulb (PI. CLXV) and m, m (PI. CLVI). The moraine is an ancient one, everywhere clothed with dense vegetation, chiefly alder and cottonwood.
The first of these is the 600 foot hill on the western side of the Copper River valley, immediately north of Childs Glacier. It is a curved ridge extending eastward a mile-and a quarter from the valley wall. Its crest everywhere rises 400 feet above sea level, or 275 feet above the adjacent valley bottom, and three knobs upon it reach elevations 100 and 200 feet higher. It connects with a 500 foot terrace on the northern slope of the valley of Childs Glacier. This terrace slopes rapidly westward to an elevation of 1200 feet. The moraine is f to ^ a mile wide and, in places, its surface has pronounced minor irregularities. Its slopes are very steep.
This moraine remnant was at first thought to be a rock hill, especially as it rises-much higher than any other moraine accumulation in the Copper River valley. In
i Martin, Lawrence, Alaskan Earthquakes of 1899, Bun. Geol. Soc. Amer., Vol. XXI, 1910, pp. 351-352,. 356, 864-365, 873, 374; Tarr, R. S. and Martin, Lawrence, .Professional Paper 69, U. S. Geol. Survey, 1912, pp. 49-50.
* Martin, Lawrence, op. cit., p. 401.
1 Data assembled by Maude Reid from Weather Bureau records. See unpublished thesis, University of Wisconsin, 1913.